Integrated gradient index lenses

ABSTRACT

Gradient index lenses are described that are integrated within a planar optical structure. The gradient index lens is optically coupled to a planar optical waveguide. In some embodiments, the gradient index lens with variation in index-of-refraction n one dimension is within an optical fiber. The optical fiber includes cladding at least along the edges of the central plane of the gradient index lens. Methods for forming the integrated structures are described. Further optical structures involving the gradient index lenses are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of copending U.S. patent applicationSer. No. 10/138,754 to Bryan filed on May 3, 2002, entitled “IntegratedGradient Index Lenses,” now U.S. Pat. No. 7,164,818, which claimspriority to copending U.S. Provisional Patent Application Ser. No.60/288,533 to Bryan, entitled “Optical Material With Selected Index OfRefraction,” incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to optical structures that incorporate gradientindex lenses, in which the optical structures are generally planaroptical structures, optical fiber preforms or optical fibers. In someembodiments, the gradient index lenses have an index-of-refraction thatvaries in one dimension. The invention further relates to light reactivedeposition for the formation of planar optical structures and opticalfiber preforms with gradient index lenses.

BACKGROUND OF THE INVENTION

Presently used optical communication light wavelengths are from 1.3 to1.6 microns. Optical waveguides, in fiber or planar form, generally havedimensions many times the wavelength. Thus, optical structures undertypical present configurations can have dimensions from a few microns toabout 100 microns depending on optical mode requirements and otherfactors. Optical transmission generally is based on transmission througha higher index-of-refraction material in a core that is surrounded by alower index-of-refraction material called the cladding. Light isconfined within the core material in appropriate geometries by totalinternal reflection at the dielectric interface for light propagatingthrough the core. Long range optical communications generally arecarried on optical fibers. However, manipulation of the optical signalsinvolves optical devices that connect with the optical fibers. Planarstructures can present optical devices in a more compact format.

An explosion of communication and information technologies comprisingInternet based systems has motivated a worldwide effort to implementoptical communication networks to take advantage of a large bandwidthavailable with optical communication. The capacity of optical fibertechnology can be expanded further with implementation of WavelengthDivision Multiplexing technology. With increasing demands, more channelsare needed to fulfill the system functions.

Basic characteristics of optical materials comprise surface quality,uniformity and optical quality. Optical quality refers to small enoughabsorption and scattering loss to achieve desired levels oftransmission. Optical quality also comprises the uniformity of opticalproperties, such as index-of-refraction, and bi-refringence properties.In addition, optical quality is affected by interface quality, such asthe interface between the core layers and cladding layers. For silica(SiO₂) and several other materials, preferred forms for opticaltransmission are a glass, while for some other materials single crystalor polycrystalline forms may have the highest quality opticaltransmission.

Several approaches have been used and/or suggested for the deposition ofthe optical materials. These approaches comprise, for example, flamehydrolysis deposition, chemical vapor deposition, physical vapordeposition, sol-gel chemical deposition and ion implantation. Flamehydrolysis deposition involves the use of a hydrogen-oxygen flame toreact gaseous precursors to form particles of the optical material as acoating on the surface of the substrate. Subsequent heat treatment ofthe coating can result in the formation of a uniform optical material,which generally is a glass material. Flame hydrolysis and forms ofchemical vapor deposition have been successful in the production ofglass for use as fiber optic elements and planar waveguides.

SUMMARY OF THE INVENTION

In a first aspect, the invention pertains to a planar optical structurecomprising a first planar optical waveguide and a first planar gradientindex lens optically coupled to the planar optical waveguide.

In another aspect, the invention pertains to an optical fiber comprisinga first gradient index lens and a cladding. The first gradient indexlens has an index-of-refraction varying in a single dimension relativeto a central plane along a first axis, and the cladding is located atleast along the edges of the central plane. The cladding has anindex-of-refraction lower than the gradient index lens along the centralplane.

In a further aspect, the invention pertains to a method for forming aplanar optical structure. The method comprises forming a core layer of aplanar optical waveguide in optical communication with a planar gradientindex lens.

In additional embodiments, the invention pertains to an opticalstructure comprising a first optical core, a second optical core, agradient index lens and a free space optical element. The first opticalcore, the second optical core and gradient index lens are within amonolithic optical structure, and the free space optical element iswithin a cut out in the monolithic optical structure. The gradient indexlens optically connects the first optical structure, and the free spaceoptical element optically connects the first optical core and the secondoptical core.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view of a reaction chamber for performinglaser pyrolysis synthesis of powders at high production rates.

FIG. 2 is a schematic representation of a reactant delivery system forthe delivery of vapor/gas reactants to a flowing reaction system, suchas the laser pyrolysis reactor of FIG. 1.

FIG. 3 is a sectional side view of a reactant inlet nozzle with anaerosol generator for the delivery of aerosol and gas/vapor compositionsinto a reaction chamber, wherein the cross section is taken along line3-3 of the insert. The insert shows a top view of an elongated reactantinlet.

FIG. 4 is a sectional side view of the reactant inlet nozzle of FIG. 3taken along the line 4-4 of the insert in FIG. 3.

FIG. 5 is a schematic diagram of a light reactive deposition apparatusformed with a particle production apparatus connected to a separatecoating chamber through a conduit.

FIG. 6 is a perspective view of a coating chamber where the walls of thechamber are transparent to permit viewing of the internal components.

FIG. 7 is perspective view of a particle nozzle directed at a substratemounted on a rotating stage.

FIG. 8 is a schematic diagram of a light reactive deposition apparatusin which a particle coating is applied to a substrate within theparticle production chamber.

FIG. 9 is a perspective view of a reactant nozzle delivering reactantsto a reaction zone positioned near a substrate.

FIG. 10 is a sectional view of the apparatus of FIG. 9 taken along line10-10.

FIG. 11 is a perspective view of an embodiment of a light reactivedeposition chamber.

FIG. 12 is an expanded view of the reaction chamber of the lightreactive deposition chamber of FIG. 11.

FIG. 13 is an expanded view of the substrate support of the reactionchamber of FIG. 12.

FIG. 14 is a perspective view of a gradient index lens with a radiallyvarying index-of-refraction.

FIG. 15 is a schematic sectional side view indicating a trajectorycorresponding to an object at infinity through a gradient index lenshaving a pitch value of 0.25.

FIG. 16 is a schematic sectional side view indicating a trajectorycorresponding to an object at the front surface of the lens through agradient index lens having a pitch value of 0.5.

FIG. 17 is a schematic sectional side view indicating a trajectorycorresponding to an object at infinity through a gradient index lenshaving a pitch value of 0.75.

FIG. 18 is a schematic sectional side view indicating a trajectorycorresponding to an object at the front surface of the lens through agradient index lens having a pitch value of 1.0.

FIG. 19 is a schematic perspective view of a one-dimensional gradientindex lens on a substrate surface with a central plane parallel to thesubstrate surface.

FIG. 20 is a schematic perspective view of a one-dimensional gradientindex lens on a substrate surface with a central plane perpendicular tothe substrate surface.

FIG. 21 is a schematic perspective view of a optical fiber with anintegrated gradient index lens.

FIG. 22 is top view of a gradient index lens integrated into a planaroptical circuit.

FIG. 23 is a fragmentary sectional view of one embodiment of aone-dimensional gradient index lens with a central plane parallel to thesubstrate surface, in which the cross section is taken along line A-A ofFIG. 22.

FIG. 24 is a fragmentary sectional view of another embodiment of aone-dimensional gradient index lens with a central plane perpendicularto the substrate surface, in which the cross section is taken along lineA-A of FIG. 22.

FIG. 25 is a fragmentary sectional view of another embodiment of atwo-dimensional gradient index lens with a radial variation inindex-of-refraction, in which the cross section is taken along line A-Aof FIG. 22.

FIG. 26 is a schematic perspective view of a planar optical circuit withtwo integrated gradient index lenses.

FIG. 27 is a schematic sectional view of an optical structure with afree space optical element optically connected to two integratedgradient index lenses.

DETAILED DESCRIPTION OF THE INVENTION

Gradient index lenses provide a versatile approach for the focusing oflight within an integrated optical structure, which can be, for example,a planar optical structure and/or an optical fiber. Gradient indexlenses involve variation in index-of-refraction at an angel to thepropagation direction of the light. Traditional gradient index lensesinvolve radial variation in index-of-refraction according to aparticular formula, which can result in the focusing of light comparableto a concave lens. In addition, a comparable variation along onedimension can result in focusing of light along one dimension, e.g.,comparable to a cylindrical lens. Gradient index lenses offer distinctadvantages over lenses formed with curved surfaces with respect tointegration of optical devices. Specifically, gradient index lenses canbe directly integrated into an optical structure during the formation ofthe optical structure. Thus, there are no complications regardingplacement, and alignment of the lens and the interface formed at thelens surface. Gradient index lenses can be formed within planar opticalstructures and optical fiber preforms, for example, by light reactivedeposition.

Fiber optic communication networks provide broadband communicationchannels. However, manipulation of the optical signals requires theinterface of the fiber optical pathways with appropriate optical devicesand electro-optical devices. The connection between different opticalelements can present significant challenges, and the ability to focuswith within an integrated structure can facilitate the connection ofdifferent elements. The formation of planar optical devices on asubstrate surface has been used to decrease the size of the opticaldevices. The formation of planar optical devices involves themanipulation of optical materials to form structures in layers withdimension on the order of a micron to tens or hundreds of microns.Improved processes for the deposition of optical materials and/or themanipulation of optical materials in the formation of optical devicesintroduces the capability of producing more complex optical devices andintegrated structures in more compact configurations.

While the discussion herein focuses on planar optical devices, some ofthe embodiments relate to optical fibers and optical fiber preforms.Optical fibers are generally formed by pulling the optical fiber from asoftened preform that introduces the basic structural and compositionalaspects of the fiber. Optical fiber preforms can be produced usingsimilar approaches for the formation of planar optical devices.

Central to the formation of optical devices is the variation of theoptical properties at different physical locations. For example,variation in index-of-refraction generally is used to confine lightalong a particular path or waveguide. Optical properties can be variedwith changes in chemical composition and/or in physical properties, suchas density.

A gradient index lens can have a radial gradient in index-of-refraction.Specifically, the index-of-refraction is largest in the center of thelens and decreases with distance radially from an axis passing throughthe center. Light propagates through the lens with a propagationcomponent along the central axis of the lens. In some embodiments, thedistribution of index-of-refraction of an ideal gradient index lens as afunction of radial distance r from the central axis can be given asN(r)=N₀(1−A r²/2), where A is the radial constant. N₀ is the maximumindex-of-refraction of the lens at the center r=0. As described by thisequation, the index-of-refraction decreases quadratically as a functionof radial distance. Of course, actual gradient index lenses onlyapproximate this distribution. An actual distribution approximating thisquadratic distribution can be continuous or a step wise discontinuouschange.

In contrast, with conventional gradient index lenses, alternativegradient index lenses have a gradient in index-of-refraction in only asingle dimension. Thus, these one-dimensional gradient index lenses onlyrefract light in a single dimension. Since they only refract light in asingle dimension, these 1-D gradient index lenses function analogouslyto a cylindrical lens. The optical material in these one-dimensionalgradient index lenses have an index of refraction that varies withdistance from a plane rather than as a radial distance. With anindex-of-refraction that only varies in a single dimension, a distance“d” from a central plane replaces the radial distance in the functionaldependence. For a gradient index lens that approximates a cylindricallens, e.g., a concave cylindrical lens, the equation describing theindex-of-refraction is N(d)=N₀(1−B d²/2), where B is the correspondingconstant related to the variation in index with distance from thecentral plane of the lens. As with the traditional two-dimensionalgradient index lenses, actual one-dimensional gradient index lenses canvary from the ideal described by the equation.

While the quadratic variation with distance for the two-dimensional andone-dimensional gradient index lenses provides an optical performancecorresponding, respectively, to concave and cylindrical lenses, otherfunctional variations in index-of-refraction as a function of radialdistance or distance from the central plane can be used to achieve otheroptical properties. The optical effect of other functional variations inindex-of-refraction can be determined from standard optical principles.A person of ordinary skill in the art can therefore select a variationin index of refraction to accomplish desired optical properties.

In some embodiments, the gradient index lenses are integrated into anoptical structure in which the gradient index lens is in opticalcommunication with other devices of the optical structure. The opticalstructure can be for example, a planar optical structure or an opticalfiber. Generally, for these integrated embodiments, the gradient indexlens can form a core that is surrounded by a cladding optical materialwith a lower index-of-refraction than the core, although the naturaldrop in index-of-refraction due to the index gradient can obviate theneed for a separate cladding. In some embodiments, a separate claddingmay be included only around selected portions of the gradient indexlens. For example, for embodiments in which the gradient varies in onedimension, the cladding can be places along edges perpendicular to thecentral plane of the gradient index lens.

Optical devices generally are formed to included confined opticalpathways or waveguides that direct light. Optical circuits can includeone or more optical devices that manipulate the light generally withpassive waveguides directing the light within the circuit, such as toand from the optical devices. Optical waveguides and many opticaldevices include a core of material confined within a cladding. The corehas a higher index-of-refraction than the surrounding cladding such thatlight is confined in the core by total internal reflection. In addition,for particular wavelengths of light, the difference inindex-of-refraction between the core and cladding is selected to bewithin a particular range to confine the light while limiting the lightto a single mode of transmission. Since planar optical materials aregenerally organized in layers, the cladding surrounding a particularwaveguide/optical device can generally be considered as including anunder-cladding in a layer below the core, an over-cladding in a layerabove the core and cladding patterned within the same layer as the coreto fill in the core layer around the core and other optical ornon-optical devices within the layer. The cladding in the core layer mayor may not be deposited during the formation of the over-cladding layer.

Efficient approaches have been developed for the patterning of opticalcompositions for the formation of optical materials, as described indetail below. For example, in the formation of a core layer, andoptionally in the formation of cladding layers, the composition of theoptical material can be varied to change the index-of-refraction and/orthe other optical properties, for example, in the formation of activeoptical devices. These approaches can be adapted for the formationplanar integrated gradient index lenses and/or optical fiber preformscomprising integrated gradient index lenses that can be pulled to formcorresponding optical fibers.

A new process has been developed involving reactive deposition driven bya radiation beam (e.g., a light beam), to form coatings with opticalcharacteristics that are tightly controlled. The coating can be used toform optical structures with simple or complex collections ofcorresponding optical devices. In one embodiment, reactive depositiondriven by a radiation beam (e.g., a light beam) involves a reactor witha flowing reactant stream that intersects a radiation beam proximate areaction zone to form a product stream configured for the deposition ofproduct particles onto a surface following formation of the particles inthe flow. The particles are deposited in the form of a powder array,i.e. a collection of unfused particles or a network of fused or partlyfused particles in which at least some characteristics of the initialprimary particles are reflected within the array. Radiation-basedreactive deposition incorporates features of a radiation-based processfor driving the reaction of a flowing reactant stream to form submicronpowders into a direct coating process. When particle formationincorporates an intense light beam as the radiation source for theharvesting of particles, the radiation-based process for the productionof submicron powders in a flow is known as laser pyrolysis. Inparticular, a wide range of reaction precursors can be used to generatea reactant stream with compositions in gas, vapor and/or aerosol form,and a wide range of highly uniform product particles can be efficientlyproduced. Reactant delivery approaches developed for laser pyrolysis canbe adapted for radiation-based reactive deposition. For convenience,this application refers to radiation-based pyrolysis and laser pyrolysisinterchangeably and to radiation-based reactive deposition and lightreactive deposition interchangeably.

In laser pyrolysis, the reactant stream is reacted by an intense lightbeam, such as a laser beam, which heats the reactants at a very rapidrate. While a laser beam is a convenient energy source, other intenseradiation (e.g., light) sources can be used in laser pyrolysis. Laserpyrolysis provides for formation of phases of materials that aredifficult to form under thermodynamic equilibrium conditions. As thereactant stream leaves the light beam, the product particles are rapidlyquenched. The reaction takes place in a confined reaction zone at theintersection of the light beam and the reactant stream. For theproduction of doped materials and other complex optical materials, thepresent approaches have the advantage that the composition of thematerials can be adjusted over desirable ranges.

Submicron inorganic particles with various stoichiometries,non-stoichiometric compositions and crystal structures, including, forexample, amorphous structures, have been produced by laser pyrolysis,alone or with additional processing, such as heat treatment.Specifically, amorphous and crystalline submicron and nanoscaleparticles can be produced with complex compositions using laserpyrolysis. Light reactive deposition can be used to form highly uniformcoatings of glasses, i.e., amorphous materials, and crystallinematerials (either single crystalline or polycrystalline), optionallywith dopants comprising, for example, complex blends of stoichiometricand/or dopant components. Suitable optical materials include, forexample, silicon oxide, germanium oxide, aluminum oxide, titanium oxide,telluride glasses, phosphate (P₂O₅) glass, InP, lithium niobate,combinations thereof and doped compositions thereof. Glasses have beengenerally used in optical applications, although crystalline aluminumoxide, e.g., sapphire, and crystalline SiO₂, e.g., quartz, may besuitable for optical applications at certain light wavelengths.

A basic feature of successful application of laser pyrolysis/lightreactive deposition for the production of particles and correspondingcoatings with desired compositions is generation of a reactant streamcontaining an appropriate precursor composition. In particular, for theformation of doped materials by light reactive deposition, the reactantstream can comprise host glass or crystal precursors and, optionally,dopant precursors. The reactant stream includes appropriate relativeamounts of precursor compositions to produce the optical materials withthe desired stoichiometries and dopant compositions. Also, unless theprecursors are an appropriate radiation absorber, an additionalradiation absorber is added to the reactant stream to absorbradiation/light energy for transfer to other compounds in the reactantstream. Other additional reactants can be used to adjust theoxidizing/reducing environment in the reactant stream. Formation ofdoped optical glasses with these reactive approaches can involve fewerprocessing steps than common commercial approaches for introducingdopants.

By adapting the properties of laser pyrolysis, light reactive depositionis able to deposit highly uniform, very small particles in a coating.Due to the uniformity and small size of the powders, light reactivedeposition can be used to form uniform and smooth coating surfaces. Thedesirable qualities of the particles are a result of driving thereaction with an intense light beam, which results in the extremelyrapid heating and cooling. Using light reactive deposition, siliconoxide glass coatings following heating have been formed that have a rootmean square surface roughness, as measured by atomic force microscopy,of about 0.25 to about 0.5 nm. Thus, the surfaces are smoother than arethought to be obtained by flame hydrolysis deposition and roughlycomparable to smoothness obtainable by chemical vapor deposition. Thesmooth glass coating applied by light reactive deposition was depositedat relatively high deposition rates by moving the substrate through theproduct stream.

Light reactive deposition is able to produce quality coatings at muchhigher rates than previously available. At the same time, light reactivedeposition is able to generate coatings with an extremely broad range ofcompositions by controlling reactant composition, reaction chemistry andreaction conditions, such as light intensity which can be used tocontinuously control effective temperatures in the reaction zone over awide range, such as in the range(s) from about room temperature (e.g.,20° C.) to about 3000° C. Thus, light reactive deposition has alreadydemonstrated the ability to be an efficient and effective approach forthe formation of very high quality glass coatings.

Multiple layers can be formed by additional sweeps of the substratethrough the product particle stream. Since each coating layer has highuniformity and smoothness, a large number of layers can be stacked whilemaintaining appropriate control on the layered structure such thatoptical devices can be formed throughout the layered structure withoutstructural variation adversely affecting the ability to form opticaldevices. Composition can be varied between layers, i.e., perpendicularto the plane of the structure, and/or portions of layers, within theplane of the structure, to form desired optical structures. Thus, usinglight reactive deposition possibly with other patterning approaches, itis possible to form complex structures with intricate variation ofmaterials with selectively varying compositions. Furthermore, byadapting laser pyrolysis techniques for the production of commercialquantities of powders, light reactive deposition can form high qualitycoatings at very rapid rates.

To form a uniform optical layer, a layer of amorphous particlesdeposited by light reactive deposition can be consolidated/densified. Toconsolidate the optical materials, the powders are heated to atemperature above their flow temperature. At these temperatures, thepowders density and upon cooling form a uniform layer of opticalmaterial. Substantially uniform optical materials have an opticalquality that permits transmission of light. Incorporation of desiredcomposition and/or dopants into the particles results in an opticalmaterial with a desired composition/dopants through the resultingdensified optical material directly as a result of the powderdeposition. Generally, amorphous particles can be consolidated to form aglass material, and crystalline particles, such as aluminum oxide, canbe consolidated to form a crystalline material, such as sapphire.However, in some embodiments, appropriate heating and quenching ratescan be used to consolidate an amorphous material into a crystallinelayer, either single crystalline or polycrystalline, (generally slowquenching rates) and a crystalline powder into a glass layer (generallya rapid quench).

Passive and/or active optical devices can be incorporated into theoptical structure to introduce the desired functionality. Opticaldevices of interest comprise, for example, optical waveguide devices,such as optical couplers, splitters, arrayed waveguide grating (AWG) andthe like. Waveguides manufactured on a substrate surface are referred toas planar waveguides. Planar waveguides are useful in the production ofintegrated optical circuits for optical communication and otheropto-electronics applications. Other optical devices of interestcomprise, for example, three dimensional optical memory device, Bragggrating, optical attenuator, optical splitter/coupler, optical filter,optical switch, laser, modulator, interconnect, optical isolator,optical add-drop multiplexer (OADM), optical amplifier, opticalpolarizer, optical circulator, phase shifter, optical mirror/reflector,optical phase-retarder, and optical detector.

Integrated optical circuits generally comprise a plurality of opticaldevices that are optically connected. In a planar optical structure, alayer of optical material can include one or more optical circuits thatform corresponding optical pathways along the layer. Due to improvedprocessing ability of light reactive deposition, multiple layer opticalstructures with multiple layers having independent light pathways havebeen described. These multiple layered optical structures are describedfurther in copending and commonly assigned PCT applicationPCT/US01/45762 designating the U.S. filed on Oct. 26, 2001 to Bi et al.,entitled “Multilayered Optical Structures,” incorporated herein byreference. Furthermore, light reactive deposition can be adapted forfull three-dimensional integration of optical structures to takeadvantage of composition variation in three dimensions. Thus, amonolithic optical structure can be formed with full integration withinone or more layers and between layers to form a highly compact opticalstructure with the capability of complex functionality. The formation ofthree-dimensional structures is described further in copending andcommonly assigned U.S. patent application Ser. No. 10/027,906, now U.S.Pat. No. 6,952,504 to Bi et al., entitled “Three Dimensional Engineeringof Optical Structures,” incorporated herein by reference. Theindex-of-refraction selection approaches described herein can be adaptedin the formation of complex multilayered optical structures by designingthe structures for light pathways to the photosensitive material forindex-of-refraction selection or by performing the index-of-refractionselection on intermediate structures before all of the layers of thestructure are deposited.

The gradient index lenses provide a convenient approach for theformation of integrated optical structures. The use of a gradient indexlens provides for convenient integration with a device capable offocusing light without the use of lenses based on curved surfaces. Thegradient index lenses can be formed as an integral part of an integratedstructure, which can be formed along other optical devices within theoptical structure. In contrast with conventional lenses with curvedsurfaces, gradient index lenses avoid placement, alignment and interfaceissues if they are formed as integral optical components within amonolithic optical structure. The specific optical properties for thegradient index lens can be selected based on the design of the gradientindex lens.

Gradient index lenses (GRIN lenses) offer a convenient alternative tothe formation of conventional lenses requiring the polishing of surfacesto obtain desired curvatures. Gradient index lenses can smoothly andcontinuously redirect light rays toward a point of focus. Simple andcompact lens geometries are possible since surface curvatures are notneeded for light focusing. Using gradient index lenses, real images canbe formed on the surface of a lens. This ability creates uniquepossibilities for coupling light into an optical fiber or relaying animage through other optical elements. Gradient index lenses areparticularly convenient for integrating the lenses into integratedoptical circuits either in an optical fiber or a planar opticalstructure.

In summary, gradient index (GRIN) lenses for integrated opticalstructures have several significant advantages. First, enablement isensured since the lens and adjacent optical structures, such as awaveguide, are formed an a monolith single structure. Thus, a separatelens does not have to be aligned mechanically, generally to submicrontolerances in the case of a single-mode waveguide. Less thermal drift isobtained since the lens and the accompanying optical devices, such as aconnected waveguide, can be made from very similar materials on a commonsubstrate. The cost generally is reduced since several parts andassembly steps can be eliminated. If the lens allows enlargement of thewaveguide at the input or output aperture, the surface qualityrequirements may be reduced for that edge since a particular defectblocks or scatters a smaller fraction of the light and results in lessinsertion loss than it would in a smaller aperture.

Particle Deposition

In embodiments of particular interest, the optical layers are formed bylight reactive deposition, although the optical materials for thegradient index lens can be deposited by other approaches, such as flamehydrolysis, chemical vapor deposition and physical vapor deposition. Inlight reactive deposition, highly uniform flow of product particles isformed that are directed toward a substrate to be coated. The resultingparticle coating can be formed into an optical material, such as a glassor crystal.

Light reactive deposition/radiation-based reactive deposition is acoating approach that uses an intense radiation source, e.g., lightsource, to drive synthesis of desired compositions from a flowingreactant stream. Light reactive deposition can result in deposition ofpowders, although hot particles deposited on the surface can partly fuseduring the deposition process due to their temperature. Generally,particles in a product flow, as described herein, can be solidparticles, liquid particles and softened particles that have not cooledsufficiently to completely solidify. Light reactive deposition hassimilarities with laser pyrolysis for powder synthesis in that anintense radiation beam (e.g., a light beam) drives the reaction. Laserpyrolysis involves a flowing reactant stream that intersects with theradiation beam at a reaction zone where reaction products formparticles. While the particles produced in laser pyrolysis are collectedfor subsequent use, in light reactive deposition, the resultingcompositions are directed to a substrate surface where a coating isformed. The characteristics of laser pyrolysis that can lead to theproduction of highly uniform particles can be correspondinglyimplemented in the production of coatings with high uniformity.

In light reactive deposition, the coating of the substrate can beperformed in a coating chamber separate from the reaction chamber or thecoating can be performed within the reaction chamber. In either of theseconfigurations, the reactant delivery system can be configured similarlyto a reactant delivery system for a laser pyrolysis apparatus for theproduction of particles with various compositions. Thus, a wide range ofcoatings can be formed for further processing into optical materials.

If the coating is performed in a coating chamber separate from thereaction chamber, the reaction chamber is essentially the same as thereaction chamber for performing laser pyrolysis, although the reactantthroughput and the reactant stream size may be designed to beappropriate for the coating process. For these embodiments, the coatingchamber and a conduit connecting the coating chamber with the reactionchamber replace the collection system of the laser pyrolysis system. Ifthe coating is performed within the reaction chamber, a substrateintercepts flow from the reaction zone, directly capturing the particlesonto its surface.

A laser pyrolysis apparatus design incorporating an elongated reactantinlet has been developed that facilitates production of commercialquantities of particles. Specifically, the reaction chamber and reactantinlet are elongated significantly along the light beam to provide for anincrease in the throughput of reactants and products. By orienting thelight beam along the elongated reactant stream, a sheet of productparticles is generated. This design has been described in U.S. Pat. No.5,958,348 to Bi et al., entitled “Efficient Production of Particles byChemical Reaction,” incorporated herein by reference.

Additional embodiments and other appropriate features for commercialcapacity laser pyrolysis apparatuses are described in copending andcommonly assigned U.S. patent application Ser. No. 09/362,631 to Mossoet al., entitled “Particle Production Apparatus,” incorporated herein byreference. The delivery of gaseous/vapor reactants and/or aerosolreactants, as described further below, can be adapted for the elongatedreaction chamber design. These designs for commercial production ofpowders by laser pyrolysis can be adapted for rapid coating of highquality optical materials by light reactive deposition. The size of theelongated reactant inlet can be selected based on the size of thesubstrate to be coated. In some embodiments, the reactant inlet issomewhat larger than the diameter or other dimension across thesubstrate, such as a width, such that the entire substrate can be coatedin one pass through the product stream. In other embodiments, thesubstrate is placed far enough away from the reactant inlet that theproduct particle stream spreads significantly prior to reaching thesubstrate such that a larger area of the substrate is simultaneouslycoated.

In general, the particle production apparatus with the elongatedreaction chamber and reactant inlet is designed to reduce contaminationof the chamber walls, to increase the production capacity and to makeefficient use of resources. Due to the chamber design, the elongatedreaction chamber can provide for an increased throughput of reactantsand products without a corresponding increase in the dead volume of thechamber. The dead volume of the chamber can become contaminated withunreacted compounds and/or reaction products. Furthermore, anappropriate flow of shielding gas can confine the reactants and productswithin a flow stream through the reaction chamber. The high throughputof reactants makes efficient use of the radiation (e.g., light) energy.

With light reactive deposition, the rate of particle production forrapid coating can vary, for example, in the range(s) from about 1 gramper hour of reaction product to about 10 kilograms per hour of desiredreaction product, although clearly lower rates are obtainable ifdesired. A person of ordinary skill in the art will recognize thatadditional ranges within the specific ranges are contemplated and arewithin the present disclosure. Not all of the particles generated aredeposited on the substrate. In general, the deposition efficiencydepends on several factors including, for example, the relative speed ofthe substrate through the product stream with the particles, forembodiments based on moving the substrate through a sheet of productparticles. Other factors affecting deposition efficiency include, forexample, the particle composition, particle temperature and substratetemperature. At moderate relative rates of substrate motion, coatingefficiencies of about 15 to about 20 percent have been achieved, i.e.about 15 to about 20 percent of the produced particles are deposited onthe substrate surface. Routine optimization can increase this depositionefficiency further. At slower relative motion of the substrate throughthe product particle stream, deposition efficiencies of at least about40 percent have been achieved and can be as high as 80 percent or more.A person of ordinary skill in the art will recognize that additionalembodiments within the explicit coating efficiencies are contemplatedand are within the present disclosure.

Alternatively or in addition, the invention provides that the rate ofthe movement of the substrate and the particle flow relative to eachother can vary substantially, depending on the desired specificationsfor the coated substrate. Thus, in one embodiment, the rate can bemeasured on an absolute scale, and can vary in the range(s) of at leastabout 0.001 inches per second, in other embodiments at least about 0.05inches per second, in further embodiments, from about 1 inch per secondto about 12 inches per second, or even more. A person of ordinary skillin the art will recognize that additional ranges and subranges withinthese explicit ranges are contemplated and are encompassed within thepresent disclosure.

For appropriate embodiments using a sheet of product particles, the rateof relative substrate motion generally is a function of the selecteddeposition rate and the desired coating thickness as limited by themovement the substrate at the desired rate while obtaining desiredcoating uniformity. In embodiments in which the substrate is sweptthrough the product particle stream, the substrate can be moved relativeto a fixed nozzle, or the nozzle can be moved relative to a fixedsubstrate. Due to the high deposition rates achievable with lightreactive deposition, extremely fast coating rates are easily achievable.These coating rates by light reactive deposition are dramatically fasterthan rates that are achievable by competing methods.

Furthermore, the rapid production rate can be advantageously used toform a plurality of particles coatings with or without consolidationbetween coatings. Each coating can cover an entire layer or a portion ofa layer. Compositions can be changed within a layer or between layers.When changing compositions significantly between layers, it may bedesirable to wait a few seconds for the product stream to stabilize.

The design of the elongated reaction chamber 100 for generating a sheetof product particles is shown schematically in FIG. 1. A reactant inlet102 leads to main chamber 104. Reactant inlet 102 conforms generally tothe shape of main chamber 104. Main chamber 104 comprises an outlet 106along the reactant/product stream for removal of particulate products,any unreacted gases and inert gases. Shielding gas inlets 108 arelocated on both sides of reactant inlet 102. Shielding gas inlets areused to form a blanket of inert gases on the sides of the reactantstream to inhibit contact between the chamber walls and the reactants orproducts. The dimensions of elongated reaction chamber 104 and reactantinlet 102 can be designed for highly efficiency particle production.Reasonable dimensions for reactant inlet 102 for the production ofnanoparticles, when used with a CO₂ laser with a power in the severalkilowatt range, are from about 5 mm to about 1 meter.

Tubular sections 110, 112 extend from the main chamber 104. Tubularsections 110, 112 hold windows 114, 116, respectively, to define a lightbeam path 118 through the reaction chamber 100. Tubular sections 110,112 can comprise inert gas inlets 120, 122 for the introduction of inertgas into tubular sections 110, 112.

Outlet 106 can lead to a conduit directed to a coating chamber. Thereaction zone is located within the reaction chamber. A change indimension does not necessarily demarcate a transition from the reactionchamber to a conduit to the coating chamber for appropriate embodiments.The conduit can but does not necessarily involve a change in directionof the flow. Alternatively or additionally, a substrate can interceptthe product flow to coat the substrate within the reactant chamber.

Reactant inlet 102 is generally connected to a reactant delivery system.Referring to FIG. 2, an embodiment 130 of a reactant delivery apparatuscomprises a source 132 of a precursor compound, which can be a liquid,solid or gas. For liquid or solid reactants, an optional carrier gasfrom one or more carrier gas sources 134 can be introduced intoprecursor source 132 to facilitate delivery of the reactant. Precursorsource 132 can be a liquid holding container, a solid precursor deliveryapparatus or other suitable container. The carrier gas from carrier gassource 134 can be, for example, an infrared absorber, an inert gas ormixtures thereof. In alternative embodiments, precursor source 132 is aflash evaporator that can deliver a selected vapor pressure of precursorwithout necessarily using a carrier gas.

The gases/vapors from precursor source 132 can be mixed with gases frominfrared absorber source 136, inert gas source 138 and/or gaseousreactant source 140 by combining the gases/vapors in a single portion oftubing 142. The gases/vapors are combined a sufficient distance from thereaction chamber such that the gases/vapors become well mixed prior totheir entrance into the reaction chamber. The combined gas/vapor in tube142 passes through a duct 144 into channel 146, which is in fluidcommunication with a reactant inlet, such as 102 in FIG. 1.

An additional reactant precursor can be supplied as a vapor/gas fromsecond reactant source 148, which can be a liquid reactant deliveryapparatus, a solid reactant delivery apparatus, a flash evaporator, agas cylinder or other suitable container or containers. As shown in FIG.2, second reactant source 148 delivers an additional reactant to duct144 by way of tube 142. Alternatively, second reactant source candeliver the second reactant into a second duct such that the tworeactants are delivered separately into the reaction chamber where thereactants combine at or near the reaction zone. Thus, for the formationof complex materials and/or doped materials, a significant number ofreactant sources and, optionally, separate reactant ducts can be usedfor reactant/precursor delivery. For example, as many as 25 reactantsources and/or ducts are contemplated, although in principle, evenlarger numbers could be used. Mass flow controllers 150 can be used toregulate the flow of gases/vapors within the reactant delivery system ofFIG. 2. Additional reactants/precursors can be provided similarly forthe synthesis of complex materials.

As noted above, the reactant stream can comprise one or more aerosols.The aerosols can be formed within the reaction chamber or outside of thereaction chamber prior to injection into the reaction chamber. If theaerosols are produced prior to injection into the reaction chamber, theaerosols can be introduced through reactant inlets comparable to thoseused for gaseous reactants, such as reactant inlet 102 in FIG. 1. Forthe formation of complex material, additional aerosol generators and/orvapor/gas sources can be combined to supply the desired compositionwithin the reactant stream.

An embodiment of a reactant delivery nozzle configured to deliver anaerosol reactant is shown in FIGS. 3 and 4. Inlet nozzle 160 connectswith a reaction chamber at its lower surface 162. Inlet nozzle 160comprises a plate 164 that bolts into lower surface 162 to secure inletnozzle 160 to the reaction chamber. Inlet nozzle 160 comprises an innernozzle 166 and an outer nozzle 168. Inner nozzle 166 can have, forexample, a twin orifice internal mix atomizer 170 at the top of thenozzle. Suitable gas atomizers are available from Spraying Systems,Wheaton, Ill. The twin orifice internal mix atomizer 170 has a fan shapeto produce a thin sheet of aerosol and gaseous compositions. Liquid isfed to the atomizer through tube 172, and gases for introduction intothe reaction chamber are fed to the atomizer through tube 174.Interaction of the gas with the liquid assists with droplet formation.

Outer nozzle 168 comprises a chamber section 176, a funnel section 178and a delivery section 180. Chamber section 176 holds the atomizer ofinner nozzle 166. Funnel section 178 directs the aerosol and gaseouscompositions into delivery section 180. Delivery section 180 leads to arectangular reactant opening 182, shown in the insert of FIG. 3.Reactant opening 182 forms a reactant inlet into a reaction chamber forlaser pyrolysis or light reactive deposition. Outer nozzle 168 comprisesa drain 184 to remove any liquid that collects in the outer nozzle.Outer nozzle 168 is covered by an outer wall 186 that forms a shieldinggas opening 188 surrounding reactant opening 182. Inert shielding gas isintroduced through tube 190. Additional embodiments for the introductionof an aerosol with one or more aerosol generators into an elongatedreaction chamber is described in U.S. Pat. No. 6,193,936 to Gardner etal., entitled “Reactant Delivery Apparatuses,” incorporated herein byreference.

For the formation of oxides, suitable secondary reactants serving as anoxygen source comprise, for example, O₂, CO, N₂O, H₂O, CO₂, O₃ andmixtures thereof. Molecular oxygen can be supplied as air.Alternatively, oxygen can be provided in a metal/metalloid precursorcompound, such as a carbonyl. A secondary reactant compound, if present,should not react significantly with the metal precursor prior toentering the reaction zone since this generally would result in theformation of large particles. However, reacting precursors can bedelivered into the reactant chamber through separate nozzles such thatthe reactant do not combine until they are near the reaction zone.

Laser pyrolysis/light reactive deposition can be performed with avariety of optical frequencies, using either a laser or other strongfocused light source, such as an arc lamp. Some desirable light sourcesoperate in the infrared portion of the electromagnetic spectrum. CO₂lasers are particularly convenient sources of light. Infrared absorbersfor inclusion in the reactant stream comprise, for example, C₂H₄, water,isopropyl alcohol, NH₃, SF₆, SiH₄ and O₃. O₃ can act as both an infraredabsorber and as an oxygen source. The radiation absorber, such as theinfrared absorber, absorbs energy from the radiation beam anddistributes the energy to the other reactants to drive the reaction.

Generally, the energy absorbed from the light beam increases thetemperature at a tremendous rate, many times the rate that heatgenerally would be produced by exothermic reactions under controlledcondition. While the process generally involves nonequilibriumconditions, the temperature can be described approximately based on theenergy in the absorbing region. In light reactive deposition, thereaction process is qualitatively different from the process in acombustion reactor where an energy source initiates a reaction, but thereaction is driven by energy given off by an exothermic reaction. In acombustion reactor, there is generally no well-defined reaction zonewith a boundary. The reaction zone is large and the residence time ofthe reactants is long. Lower thermal gradients are generally present inthe combustion reactor.

In contrast, the laser/light driven reactions have extremely highheating and quenching rates. The product compositions and particleproperties generally depend on the laser power in the reactions zone andthe quantity of radiation absorbers in the flow. By controlling thecomposition of the reactant flow and the light intensity in the reactionzone, the reaction product can be reproducibly controlled. The effectivetemperature in the reaction zone can be controlled over a wide range,for example, in the range(s) from about room temperature (e.g., 20° C.)to about 3000° C. In light reactive deposition, the reaction zone isprimarily at the overlap of the light beam and the reactant stream,although the reaction zone may extend, for example, a few millimetersbeyond the light beam, depending on the precise character of thereaction. After leaving the reaction zone in a radiation/light drivenreactor, the particles may still be somewhat fluid/soft due to theirtemperature even if the reaction has terminated.

An inert shielding gas can be used to reduce the amount of reactant andproduct molecules contacting the reactant chamber components. Inertgases can also be introduced into the reactant stream as a carrier gasand/or as a reaction moderator. Appropriate inert shielding gasescomprise, for example, Ar, He and N₂.

Laser pyrolysis apparatuses can be adapted for light reactivedeposition. The nature of the adaptation depends on whether or not thecoating is performed in the reaction chamber or within a separatecoating chamber. In any of the embodiments, the reactant delivery inletinto the reaction chamber generally is configured to deliver a reactantstream with dimensions that results in a product stream with desireddimensions for the deposition process. For example, in some embodiments,the reactant inlet has a length approximately the same size or slightlylarger than the diameter of a substrate such that the substrate can becoated along an entire dimension of the substrate with one pass throughthe product stream without wasting excessive amount of product.

The outlet of a laser pyrolysis apparatus can be adapted for the coatingof substrates within a separate coating chamber. A coating apparatuswith separate reaction chamber and coating chamber is shownschematically in FIG. 5. The coating apparatus 200 comprises a reactionchamber 202, a coating chamber 204, a conduit 206 connecting reactionchamber 202 with coating chamber 204, an exhaust conduit 208 leadingfrom coating chamber 204 and a pump 210 connected to exhaust conduit208. A valve 212 can be used to control the flow to pump 210. Valve 212can be, for example, a manual needle valve or an automatic throttlevalve. Valve 212 can be used to control the pumping rate and thecorresponding chamber pressures. A collection system, filter, scrubberor the like 214 can be placed between the coating chamber 204 and pump210 to remove particles that did not get coated onto the substratesurface.

Referring to FIG. 6, conduit 206 from the particle production apparatus202 leads to coating chamber 204. Conduit 206 terminates at opening 216within chamber 204. In some embodiments, conduit opening 216 is locatednear the surface of substrate 218 such that the momentum of the particlestream directs the particles directly onto the surface of substrate 218.Substrate 218 can be mounted on a stage or other platform 220 toposition substrate 218 relative to opening 216.

An embodiment of a stage to position a substrate relative to the conduitfrom the particle production apparatus is shown in FIG. 7. A particlenozzle 230 directs particles toward a rotating stage 232. As shown inFIG. 7, four substrates 234 are mounted on stage 232. More or fewersubstrates can be mounted on a moveable stage with correspondingmodifications to the stage and size of the chamber. A motor is used torotate stage 232. Other designs for a stage, conveyor or the like can beused to sweep the substrate through the product particle flow.

Movement of stage 232 sweeps the particle stream across a surface of oneparticular substrate 234 within the path of nozzle 230. Stage 232 can beused to pass sequential substrates through the product stream for one ormore coating applications to each substrate. Stage 232 can comprisethermal control features that provide for the control of the temperatureof the substrates on stage 232. Alternative designs involve the linearmovement of a stage or other motions. In other embodiments, the particlestream is unfocused such that an entire substrate or the desiredportions thereof is simultaneously coated without moving the substraterelative to the product flow.

If the coating is performed within the reaction chamber, the substrateis mounted to receive product compositions flowing from the reactionzone. The compositions may not be fully solidified into solid particles,although quenching may be fast enough to form solid particles. Whetheror not the compositions are solidified into solid particles, theparticles can be highly uniform. The distance from the reaction zone tothe substrate can be selected to yield desired coating results.

An apparatus 250 to perform substrate coating within the reactionchamber is shown schematically in FIG. 8. The reaction/coating chamber252 is connected to a reactant supply system 254, a radiation source 256and an exhaust 258. Exhaust 258 can be connected to a pump 260, althoughthe pressure from the reactant stream itself can maintain flow throughthe system. A valve 262 can be used to control the flow to pump 260.Valve 262 can be used to adjust the pumping rate and the correspondingchamber pressures. A collection system, filter, scrubber or the like 264can be placed between chamber 252 and pump 260 to remove particles thatdid not get coated onto the substrate surface.

Substrate 266 can contact flow from a reaction zone 268 to coat thesubstrate with product particles/powders. Substrate 266 can be mountedon a stage, conveyor, or the like 270 to sweep substrate 266 through theflow. Stage 270 can be connected to an actuator arm 272 or othermotorized apparatus to move stage 270 to sweep the substrate through theproduct stream. Various configurations can be used to sweep the coatingacross the substrate surface as the product leaves the reaction zone. Ashown in FIG. 8, actuator arm 272 translates stage 270 to sweepsubstrate 266 through the product stream.

A similar embodiment is shown in an expanded view in FIGS. 9 and 10. Asubstrate 280 moves relative to a reactant nozzle 282, as indicated bythe right directed arrow. Reactant nozzle 282 is located just abovesubstrate 280. An optical path 284 is defined by suitable opticalelements that direct a light beam along path 284. Optical path 284 islocated between nozzle 282 and substrate 280 to define a reaction zonejust above the surface of substrate 280. The hot particles tend toattract to the cooler substrate surface.

Referring to FIGS. 9 and 10, a particle coating 286 is formed as thesubstrate is scanned past the reaction zone. In general, substrate 280can be carried on a conveyor/stage 288. Conveyor/stage 288 can beconnected to an actuator arm, as shown in FIG. 8. In alternativeembodiments, rollers and a motor, a continuous belt conveyor, or any ofa variety of design, comprising known designs, for translating asubstrate can be used to carry the substrate.

In some embodiments, the position of conveyor 288 can be adjusted toalter the distance from substrate 286 to the reaction zone. Changes inthe distance from substrate to the reaction zone correspondingly alterthe temperature of the particles striking the substrate. The temperatureof the particles striking the substrate generally alters the propertiesof the resulting coating and the requirements for subsequent processing,such as a subsequent heat processing consolidation of the coating. Thedistance between the substrate and the reaction zone can be adjustedempirically to produce desired coating properties. In addition, thestage/conveyor supporting the substrate can comprise thermal controlfeatures such that the temperature of the substrate can be adjusted tohigher or lower temperatures, as desired.

A particular embodiment of a light reactive deposition apparatus isshown in FIGS. 11-13. Referring to FIG. 11, process chamber 300comprises a light tube 302 connected to a CO₂ laser (not shown) and alight tube 304 connected to a beam dump (not shown). An inlet tube 306connects with a precursor delivery system that delivers vapor reactantsand carrier gases. Inlet tube 306 leads to process nozzle 308. Anexhaust tube 310 connects to process chamber 300 along the flowdirection from process nozzle 308. Exhaust tube 310 leads to a particlefiltration chamber 312. Particle filtration chamber 312 connects to apump at pump connector 314.

An expanded view of process chamber 300 is shown in FIG. 12. A wafercarrier 316 supports a wafer above process nozzle 308. Wafer carrier 316is connected with an arm 318, which translates the wafer carrier to movethe wafer through the particle stream emanating from the reaction zonewhere the laser beam intersects the precursor stream from process nozzle308. Arm 318 comprises a linear translator that is shielded with a tube.A laser entry port 320 is used to direct a laser beam between processnozzle 308 and the wafer. Unobstructed flow from process nozzle wouldproceed directly to exhaust nozzle 322, which leads to particletransport tube 310.

An expanded view of wafer carrier 316 and process nozzle 308 is shown inFIG. 13. The end of process nozzle 308 has an opening for precursordelivery 324 and a shielding gas opening 326 around precursor opening toconfine the spread of precursor and product particles. Wafer carrier 316comprises a support 328 that connects to process nozzle 308 with abracket 330. A circular wafer 332 is held in a mount 334 such that wafer332 slides within mount 334 along tracks 336 to move wafer 332 into theflow from the reaction zone. Backside shield 338 prevents uncontrolleddeposition of particles on the back of wafer 332. Tracks 336 connect toarm 318.

The temperature of the substrate during the deposition process can beadjusted to achieve particular objectives. For example, the substratecan be cooled during the deposition process since a relatively coolsubstrate can attract the particles to its surface. However, in someembodiments, the substrate is heated, for example to about 500° C.,during the deposition process. Particles stick better to a heatedsubstrate. In addition, the particles tend to compact and fuse on aheated substrate such that a subsequent consolidation of the coatinginto a fused glass or other material is facilitated if the coating wereformed initially on a heated substrate.

The formation of coatings by light reactive deposition, silicon glassdeposition and optical devices in general are described further incopending and commonly assigned U.S. patent application Ser. No.09/715,935 to Bi et al., entitled “Coating Formation By ReactiveDeposition,” incorporated herein by reference, and in copending andcommonly assigned PCT application designating the U.S. serial numberPCT/US01/32413 to Bi et al. filed on Oct. 16, 2001, entitled “CoatingFormation By Reactive Deposition,” incorporated herein by reference.

The well-defined reactant stream as a sheet of flow leading into thereaction zone tends to spread after the reaction zone due to heat fromthe reaction. If the substrate is swept through the reaction zone nearthe reaction zone, the spreading of the flow may not be significant. Insome embodiments, it may be desirable to contact the substrate with theflow farther away from the reaction zone such that the flow has spreadsignificantly and the entire substrate or desired portion thereof can becoated simultaneously without moving the substrate. The appropriatedistance to obtain a uniform coating of particles depends on thesubstrate size and the reaction conditions. A typical distance of about15 centimeters would be suitable for a wafer with a 4-inch diameter.Then, when the composition of the product particle flow is changed intime during the deposition process, the composition of the particleschanges through the thickness of the coating. If the composition ischanged continuously, a continuous composition gradient through thelayer results. For optical materials, generally a continuous compositiongradient layer having a continuous composition change from a firstcomposition to a second composition has a thickness of no more thanabout 300 microns, in other embodiments no more than about 150 microns,in further embodiments, in the range(s) from about 500 nm to about 100microns and in still other embodiments in the range(s) from about 1micron to about 50 microns. A person of ordinary skill in the art willrecognize that other ranges and subranges within the explicit ranges arecontemplated and are encompassed within the present disclosure.

Alternatively, the composition can be changed incrementally ordiscretely to produce layers with varying composition, which can involvea gradual change in composition between two compositions or discretelayers with discrete composition differences. The resulting transitionmaterial has a step-wise change in composition from a first compositionto a second composition. Generally, the first composition and secondcomposition are the compositions of the adjacent layers such that thetransition material provides a gradual transition in composition betweenthe two adjacent layers. While an optical transition material can havetwo layers, the transition material generally has at least three layers,in other embodiments at least 4 layers and in further embodiments in therange(s) from 5 layers to 100 layers. A person of ordinary skill in theart will recognize that additional range(s) within these specific rangesare contemplated and are within the present disclosure. The totalthickness generally is similar to the continuous gradient layersdescribed in the previous paragraph. Each layer within the step-wisetransition material generally has a thickness less than about 100microns, in other embodiments less than about 25 microns, in furtherembodiments in the range(s) from about 500 nm to about 20 microns and inadditional embodiments in the range(s) from about 1 micron to about 10microns. The layers within the step-wise transition material may or maynot have approximately equal thickness. Similarly, the step-wise changein composition may or may not take equivalent steps between layers ofthe transition material.

For the production of discrete optical devices or other structures on asubstrate surface, the composition of the optical material generallymust be different at different locations within the optical structure.To introduce the composition variation, the deposition process itselfcan be manipulated to produce specific structures. Alternatively,various patterning approaches can be used following the deposition.These approaches can be adapted for the formation of gradient indexlenses.

Using the deposition approaches described herein, the composition ofproduct particles deposited on the substrate can be changed during thedeposition process to deposit particles with a particular composition atselected locations on the substrate to vary the resulting composition ofthe optical material along the x-y plane. Using light reactivedeposition, the product composition can be varied by adjusting thereactants that react to form the product particle or by varying thereaction conditions. The reactant flow can comprise vapor and/or aerosolreactants, which can be varied to alter the composition of the products.In particular, dopant concentrations can be changed by varying thecomposition and/or quantity of dopant elements in the flow. The reactionconditions can also affect the resulting product particles. For example,the reaction chamber pressure, flow rates, radiation intensity,radiation energy/wavelength, concentration of inert diluent gas in thereaction stream, temperature of the reactant flow can affect thecomposition and other properties of the product particles.

While product particle composition changes can be introduced by changingthe reactant flow composition or the reaction conditions while sweepinga substrate through the product stream, it may be desirable, especiallywhen more significant compositional changes are imposed to stop thedeposition between the different deposition steps involving thedifferent compositions. For example, to coat one portion of a substratewith a first composition and the remaining portions with anothercomposition, the substrate can be swept through the product stream todeposit the first composition to a specified point at which thedeposition is terminated. The substrate is then translated the remainingdistance without any coating being performed. The composition of theproduct is then changed, by changing the reactant flow or reactionconditions, and the substrate is swept, after a short period of time forthe product flow to stabilize, in the opposite direction to coat thesecond composition in a complementary pattern to the first composition.A small gap can be left between the coatings of the first compositionand the second composition to reduce the presence of a boundary zonewith a mixed composition. The small gap can fill in during theconsolidation step to form a smooth surface with a relatively sharpboundary between the two materials.

This process can be generalized for the deposition of more than twocompositions and/or more elaborate patterns on the substrate. In themore elaborate processes, a shutter can be used to block depositionwhile the product flow is stabilized and/or while the substrate is beingpositioned. A precision controlled stage/conveyor can precisely positionand sweep the substrate for the deposition of a particular composition.The shutter can be rapidly opened and closed to control the deposition.Gaps may or may not be used to slightly space the different location ofthe compositions within the pattern.

In other embodiments, a discrete mask is used to control the depositionof particles. A discrete mask can provide an efficient and preciseapproach for the patterning of particles. With chemical vapor depositionand physical vapor deposition, a layer of material is built up from anatomic or molecular level, which requires binding of the mask at anatomic or molecular level to prevent migration of the material beingdeposited under the mask to blocked regions. Thus, the “masks” are acoating on the surface without an independent, self-supporting structurecorresponding to the mask, and the “mask” is chemically or physicallybonded to the surface with atomic level contact along the “mask”. Incontrast, with particle deposition, the particles generally can be atleast macromolecular in size with diameters of about 3 nanometers (nm)or more such that a mask with a flat surface placed against another flatsurface provides sufficient contact to prevent significant particlemigration past the mask. The discrete masks have an intactself-supporting structure that is not bonded to the surface such thatthe mask can be removed intact from the surface that is coated.Therefore, the discrete mask approach herein is different from previousmasking approaches adapted from photolithography for vapor depositionapproaches.

The formation of the particle coating involves directing a productparticle stream at the substrate shielded with the discrete mask. Thediscrete mask has a planar surface with openings at selected locations.The discrete mask blocks the surface except at the openings such thatparticles can deposit on the surface through the openings. Thus, themask provides for patterning compositions on the surface by the selectedplacement of the openings. Suitable discrete masks comprise a mask witha slit that is narrower than the product particle flow such that thedeposition process can be very precisely controlled. Movement of theslit can form a desired, precisely controlled pattern with one or morecompositions. After use of a discrete mask, it can be removed andreused.

In some embodiments, a plurality of masks is used to deposit particlesalong a single layer. For example, following deposition of a patternthrough a first mask, a second complementary mask can be used to depositmaterial over at least a portion of the surface left uncovered duringdeposition with the first mask. Further complementary masks can be usedto form complex patterns while completing a single layer or portionthereof with a coating having varying chemical composition over thelayer.

Thus, using light reactive deposition, a range of effective approachesare available to vary the chemical composition of optical materialswithin layers and in different layers to form three-dimensional opticalstructures with selected compositions are selected locations within thematerial. In other words, the optical properties and/or composition ofthe materials can be varied along all three axes, x, y and z, within theoptical structure to form desired structures. The patterning ofcompositions of optical materials during the deposition process isdescribed further in copending and commonly assigned U.S. patentapplication Ser. No. 10/027,906, now U.S. Pat. No. 6,952,504 to Bi etal., entitled “Three Dimensional Engineering of Optical Structures,”incorporated herein by reference.

Compositions and Properties of Particles and Coatings

A variety of particles can be produced by laser pyrolysis/light reactivedeposition. Adaptation of laser pyrolysis for the performance of lightreactive deposition can be used to produce coatings of comparablecompositions as the particles with selected compositions that can beproduced by laser pyrolysis. Powders of particular interest comprise,for example, silicon particles, metal particles, and metal/metalloidcompounds, such as, metal/metalloid oxides, metal/metalloid carbides,metal/metalloid nitrides, and metal/metalloid sulfides. For opticalmaterials, some materials of particular interest comprise, for example,silicon oxide (silica), phosphate glasses, germanium oxide, InP, lithiumniobate, telluride glasses, aluminum oxide, titanium oxide, combinationsthereof and doped versions thereof. The particles can be doped to alterthe optical, chemical and/or physical properties of the particles.Generally, the powders comprise fine or ultrafine particles withparticle sizes in the submicron or nanometer range. The particles may ormay not partly fuse or sinter during the deposition.

Laser pyrolysis/light reactive deposition is particularly suitable forthe formation of highly uniform particles, especially nanoscaleparticles. In particular, laser pyrolysis can produce a collection ofparticles of interest generally with an average diameter for the primaryparticles of less than about 500 nm, alternatively in the range(s) fromabout 3 nm to about 100 nm, similarly in the range(s) from about 3 nm toabout 75 nm, and also in the range(s) from about 3 nm to about 50 nm.Persons of ordinary skill in the art will recognize that other rangesand subranges within these specific ranges are contemplated and arecovered by the present disclosure.

Laser pyrolysis/light reactive deposition, as described above, generallyresults in primary particles having a very narrow range of particlediameters. With aerosol delivery of reactants for laser pyrolysis/lightreactive deposition, the distribution of particle diameters can beparticularly sensitive to the reaction conditions. Nevertheless, if thereaction conditions are properly controlled, a very narrow distributionof particle diameters can be obtained with an aerosol delivery system.However, with aerosol and/or vapor reactants broader distributions ofprimary particles sizes can also be obtained, if desired, by controllingthe flow rates, reactant densities and residence times in laserpyrolysis/light reactive deposition or using other flowing reactionsystems.

In embodiments with highly uniform particles, effectively no primaryparticles have an average diameter greater than about 4 times theaverage diameter and in other embodiments 3 times the average diameter,and in further embodiments 2 times the average diameter. In other words,the particle size distribution effectively does not have a tailindicative of a small number of particles with significantly largersizes. An effective cut off in the tail of the size distributionindicates that there are less than about 1 particle in 10⁶ have adiameter greater than a specified cut off value above the averagediameter. Narrow size distributions, lack of a tail in the distributionsand a roughly spherical morphology can be advantageous for obtaininghighly uniform particle coatings and for highly uniform densifiedmaterials following consolidation.

Small particle size, spherical morphology and particle uniformity cancontribute overall to the uniformity of the resulting coating, forexample, with respect to composition as well as the smoothness of thesurface and interfaces between materials. In particular, the lack ofparticles significantly larger than the average, i.e., the lack of atail in the particle size distribution, leads to a more uniform coating.In addition, the particles can have a very high purity level.

When collecting the particles directly onto a substrate surface, thedistance from the substrate to the reaction zone and the temperature ofthe substrate can be adjusted to control the character of the deposit onthe substrate surface. The particles on the surface form a particlearray. The particle array can be in the form of independent primaryparticles randomly stacked on the surface. The array of primaryparticles may only be held together by electromagnetic forces betweenadjacent and nearby particles. In some embodiments, it may be desirableto form a particle array with some degree of hard fusing between primaryparticles. Fusing between primary particles can be achieved by placingthe substrate closer to the reaction zone such that the particles arenot fully quenched when they strike the substrate surface and/or byheating the substrate. Even if the primary particles are hard fused, theresulting particle array maintains character due to the nanoscale, i.e.,submicron scale, of the primary particles. In particular, primaryparticles may be visible in scanning electron micrographs. In addition,channels between the fused particles will reflect the nanoscale of thesurrounding fused particles, e.g., by having nanoscale diameter channelsextending into the powder array. Thus, the nanoscale character of theprimary particles is built into the resulting powder array formed fromthe nanoscale primary particles.

While nanoscale particles can in principle pack densely on a surface dueto their small size, the particles tend to coat a surface as a loosearray due to electrostatic forces between the particles. The relative orapparent density of the powder array can depend on the particle size,particle composition and the deposition conditions, which may affectparticle fusing as well as the forces between the particles and with thesurface. The relative density is evaluated relative to the fullydensified material of the same composition. In general, the relativedensity for the powder array formed from nanoscale particles is in therange(s) of less than about 0.6, in other embodiments in the range(s)from about 0.02 to about 0.55 and in further embodiments in the range(s)from about 0.05 to about 0.4. A person of ordinary skill in the art willrecognize that additional ranges within these specific ranges arecontemplated and are within the present disclosure.

Laser pyrolysis/light reactive deposition can be performed withgas/vapor phase reactants. Many metal/metalloid precursor compounds canbe delivered into the reaction chamber as a vapor. Metalloids areelements that exhibit chemical properties intermediate between orinclusive of metals and nonmetals. Metalloid elements include, forexample, silicon, boron, arsenic, antimony, and tellurium. Whilephosphorous is located in the periodic table near the metal elements, itis not generally considered a metalloid element. However, phosphorous inthe form of P₂O₅ is a good glass former similar to some metalloidoxides, and doped forms of P₂O₅ can have desirable optical properties.For convenience, as used herein comprising in the claims, phosphorous isalso considered a metalloid element. Appropriate metal/metalloidprecursor compounds for gaseous delivery generally comprise metalcompounds with reasonable vapor pressures, i.e., vapor pressuressufficient to get desired amounts of precursor gas/vapor into thereactant stream. The vessel holding liquid or solid precursor compoundscan be heated to increase the vapor pressure of the metal precursor, ifdesired. Solid precursors generally are heated to produce a sufficientvapor pressure by sublimation or by melting the solid into a liquid.

As an example of suitable precursors for optical material formation,representative silicon precursors for vapor delivery comprise, forexample, silicon tetrachloride (SiCl₄), trichlorosilane (Cl₃HSi),trichloromethyl silane CH₃SiCl₃, tetramethoxysilane (Si(OCH₃)₄) andtetraethoxysilane (Si(OC₂H₅)₄, also known as ethyl silane and tetraethylsilane).

Suitable dopants for silicon oxide materials include, for example,boron, germanium, phosphorous, titanium, tin, zinc and aluminum.Suitable boron precursors for gas/vapor delivery include, for example,boron trichloride (BCl₃), diborane (B₂H₆), tetraethoxyboride and BH₃.Suitable phosphorous precursors for gas/vapor delivery include, forexample, phosphine (PH₃), tetraethoxyphosphide, phosphorus trichloride(PCl₃), phosphorus oxychloride (POCl₃) and P(OCH₃)₃. Suitable germaniumprecursors for gas/vapor delivery include, for example,tetraethoxygermanate, GeCl₄. Suitable titanium precursors for gas/vapordelivery include, for example, titanium tetrachloride (TiCl₄), andtitanium isopropoxide (Ti[OCH(CH₃)₂]₄). Suitable tin precursors include,for example, SnCl₄ and liquid organometallic tin compounds such as(C₄H₉)SnCl₃ (n-butyl tin trichloride), (CH₂CH)₂ SnCl₂ (divinyl tindichloride) and (C₄H₉)₃ SnCl (tri-n-butyl tin chloride). Suitable liquidzinc precursor compounds for gas/vapor delivery include, for example,diethyl zinc (Zn(C₂H₅)₂) and dimethyl zinc (Zn(CH₃)₂). Suitable solid,zinc precursors with sufficient vapor pressure of vapor deliveryinclude, for example, zinc chloride (ZnCl₂). Suitable liquid, aluminumprecursors for gas/vapor delivery include, for example, aluminums-butoxide (Al(OC₄H₉)₃). A number of suitable solid, aluminum precursorcompounds are available including, for example, aluminum chloride(AlCl₃), aluminum ethoxide (Al(OC₂H₅)₃), and aluminum isopropoxide(Al[OCH(CH₃)₂]₃). Suitable germanium precursors for aerosol deliverycomprise, for example, Ge(OC₂H₅)₃, Ge(OCH₃)₄, and the like, and suitablecombinations of any two or more thereof. Precursors for other additives,dopants and host materials can be similarly selected based on analogywith these specific precursors.

The use of exclusively gas phase reactants is somewhat limiting withrespect to the types of precursor compounds that can be usedconveniently. Thus, techniques can be used to introduce aerosolscontaining reactant precursors to the reaction zone. Suitable aerosoldelivery apparatuses adapted for performing light reactive depositionare described above.

Using aerosol delivery apparatuses, solid precursor compounds can bedelivered by dissolving the compounds in a solvent. Alternatively,powdered precursor compounds can be dispersed in a liquid/dispersant foraerosol delivery. Liquid precursor compounds can be delivered as anaerosol from a neat liquid, a multiple liquid dispersion or a liquidsolution. A solvent/dispersant can be selected to achieve desiredproperties of the resulting solution/dispersion. While a particularsolvent/dispersant can be selected based on the precursors and otherreaction parameters, suitable solvents/dispersants generally include,for example, water, methanol, ethanol, isopropyl alcohol, other organicsolvents and mixtures thereof. The solvent should have a desired levelof purity such that the resulting particles have a desired purity level.Some solvents, such as isopropyl alcohol, are significant absorbers ofinfrared light from a CO₂ laser such that no additional laser absorbingcompound may be needed within the reactant stream if a CO₂ laser is usedas a light source.

If aerosol precursors are used, the liquid solvent/dispersant can berapidly evaporated by the light beam in the reaction chamber such that agas phase reaction can take place. Thus, the fundamental features of thelaser pyrolysis/light reactive deposition reaction may be unchanged bythe presence of an aerosol. Nevertheless, the reaction conditions can beaffected by the presence of the aerosol.

A number of suitable solid precursor compounds can be delivered as anaerosol from solution. As an example of suitable aerosol precursors foroptical materials, suitable silicon precursors for aerosol productioncomprise, for example, silicon tetrachloride Si(Cl₄), which is solublein ether, and trichlorosilane (Cl₃HSi), which is soluble in carbontetrachloride. Suitable silicon oxide dopants also can be delivered inan aerosol. Stannous chloride (SnCl₂) is soluble in alcohol. Forexample, zinc chloride (ZnCl₂) and zinc nitrate (Zn(NO₃)₂) are solublein water and some organic solvents, such as isopropyl alcohol.Similarly, a boron dopant can be delivered as an aerosol using ammoniumborate ((NH₄)₂B₄O₇), which is soluble in water and various organicsolvents. Precursors for other dopants and host materials can besimilarly selected based on analogy with these specific precursors.

The precursor compounds for aerosol delivery can be dissolved in asolution generally with a concentration greater than about 0.1 molar.For a particular aerosol flow rate, the greater the concentration ofprecursor in the solution the greater the throughput of reactant throughthe reaction chamber. As the concentration increases, however, thesolution can become more viscous such that the aerosol may have dropletswith larger sizes than desired. Thus, selection of solutionconcentration can involve a balance of factors in the selection of adesired solution concentration.

Several different types of nanoscale particles have been produced bylaser pyrolysis. Similar particles can be produced for light reactivedeposition based on the description above. Such nanoscale particles forlight reactive deposition can generally be characterized as comprising acomposition comprising a number of different elements that are presentin varying relative proportions, where the number and the relativeproportions are selected based on the application for the nanoscaleparticles. Materials that have been produced (possibly with additionalprocessing, such as a heat treatment) or have been described in detailfor production by laser pyrolysis/light reactive deposition include, forexample, amorphous SiO₂, doped SiO₂, crystalline silicon dioxide,titanium oxide (anatase and rutile TiO₂), MnO, Mn₂O₃, Mn₃O₄, Mn₅O₈,vanadium oxide, silver vanadium oxide, lithium manganese oxide, aluminumoxide (γ-Al₂O₃, delta-Al₂O₃ and theta-Al₂O₃), doped-crystalline andamorphous alumina, tin oxide, zinc oxide, rare earth metal oxideparticles, rare earth doped metal/metalloid oxide particles, rare earthmetal/metalloid sulfides, rare earth doped metal/metalloid sulfides,silver metal, iron, iron oxide, iron carbide, iron sulfide (Fe_(1-x)S),cerium oxide, zirconium oxide, barium titanate (BaTiO₃), aluminumsilicate, aluminum titanate, silicon carbide, silicon nitride, andmetal/metalloid compounds with complex anions, for example, phosphates,silicates and sulfates. In particular, many materials suitable for theproduction of optical materials can be produced by light reactivedeposition. The production of particles by laser pyrolysis andcorresponding deposition by light reactive deposition having ranges ofcompositions is described further in copending and commonly assignedU.S. patent application Ser. No. 10/027,906, now U.S. Pat. No. 6,952,504to Bi et al., entitled “Three Dimensional Engineering of OpticalStructures,” incorporated herein by reference.

Submicron and nanoscale particles can be produced with selected dopantsusing laser pyrolysis and other flowing reactor systems. Amorphouspowders and glass layers can be formed with complex compositionscomprising a plurality of selected dopants. The powders can be used toform optical materials and the like. The glass layers can be formed bydirectly depositing a uniform particle coating using light reactivedeposition and subsequently consolidating the powder into a uniformglass layer. Amorphous submicron and nanoscale powders and glass layerswith complex compositions having multiple metal/metalloid elementsand/or dopants, such as rare earth dopants and/or other metal dopants,are described further in copending and commonly assigned U.S. patentapplication Ser. No. 10/099,597 filed on Mar. 15, 2002, now U.S. Pat.No. 6,849,334 to Home et al., entitled “Optical Materials And OpticalDevices,” incorporated herein by reference.

Additives and/or dopants can be introduced at desired stoichiometries byvarying the composition of the reactant stream. Any additives/dopantsare introduced into an appropriate host glass forming material. Byappropriately selecting the composition in the reactant stream and theprocessing conditions, submicron particles incorporating one or moremetal or metalloid elements as glass-forming hosts with selectedadditives and/or dopants, including, for example, rare earth dopantsand/or complex blends of dopant compositions, can be formed. Since thehost amorphous materials generally are oxides, an oxygen source shouldalso be present in the reactant stream. The conditions in the reactorshould be sufficiently oxidizing to produce the oxide materials.

Additives/dopants can be introduced to vary properties of the amorphousparticles and/or a resulting glass layer. For example, additives/dopantscan be introduced to change the index-of-refraction of the glass. Foroptical applications, the index-of-refraction can be varied to formspecific optical devices that operate with light of a selected frequencyrange. Additives/dopants can also be introduced to alter the processingproperties of the material. In particular, some additives/dopants changethe flow temperature, i.e., the glass transition temperature, such thatthe glass can be processed at lower temperatures. In particular, boronand phosphorous elements can help to lower the viscosity and thereforethe flow temperature of silicon oxide. Lowering the flow temperature canbe desirable for reducing stress and the attendant birefringence and forimproving the consolidation of multiple layers where lower flowtemperature materials are placed on top of existing coatings. Borondopants also lowers the index-of-refraction of silica glass whilephosphorous dopants raise the index-of-refraction of silica glass.Additives/dopants can also interact within the materials. For example,some additives/dopants are introduced to increase the solubility ofother elements/compounds.

Some particles of interest comprise amorphous compositions that formoptical glasses with a plurality of additives/dopants such that thevarious properties can be selected as desired. In some embodiments, theone or plurality of dopants are rare earth metals or rare earth metalswith one or more other dopant elements. Rare earth metals comprise thetransition metals of the group IIIb of the periodic table. Specifically,the rare earth elements comprise Sc, Y and the Lanthanide series. Othersuitable dopants comprise elements of the actinide series. For opticalglasses, the rare earth metals of particular interest as dopantscomprise, for example, Ho, Eu, Ce, Tb, Dy, Er, Yb, Nd, La, Y, Pr and Tm.Generally, the rare earth ions of interest have a +3 ionization state,although Eu⁺² and Ce⁺⁴ are also of interest. Rare earth dopants caninfluence the optical absorption properties that can alter theapplication of the materials for the production of optical amplifiersand other optical devices. Suitable non-rare earth metal dopants foroptical glasses comprise, for example, Bi, Sb, Zr, Pb, Li, Na, K, Ba, B,Ge, W, Co, Ca, Cr, Ga, Al, Mg, Sr, Zn, Ti, Ta, Nb, Mo, Th, Cd and Sn.

In addition, suitable metal oxide additives/dopants for aluminum oxidefor optical glass formation comprise cesium oxide (Cs₂O), rubidium oxide(Rb₂O), thallium oxide (Tl₂O), lithium oxide (Li₂O), sodium oxide(Na₂O), potassium oxide (K₂O), beryllium oxide (BeO), magnesium oxide(MgO), calcium oxide (CaO), strontium oxide (SrO) and barium oxide(BaO). Aluminum oxide additives/dopants can affect, for example, theindex-of-refraction, consolidation temperature and/or the porosity ofthe glass.

Material processing remains a significant consideration in the design ofdesired optical devices. For example, the composition and properties,such as density, of a material are adjusted to obtain materials with adesired index-of-refraction. Similarly, the thermal expansion and flowtemperatures of a material have to be consistent with a reasonableprocessing approach for forming the materials into a monolithic,integrated structure without excessive stress that can introduceundesirable optical properties such as unintentional birefringence. Theconsolidated optical materials can provide high transparency andhomogeneity at the operating wavelength such that light transmissionthrough the materials does not result in undesirable amount of loss. Inaddition, the materials have to be processable under reasonableconditions to form the integrated devices of integrated optical circuitsor electro-optical circuits.

To obtain particular objectives, the features of the coating can bevaried with respect to composition of layers of the powders as well aslocation of materials on the substrate. Generally, to form an opticaldevice an optical material can be localized to a particular location onthe substrate. In addition, multiple layers of particles can bedeposited in a controlled fashion to form layers with differentcompositions and/or optical properties. Similarly, the coating can bemade a uniform thickness, or different portions of the substrate can becoated with different thicknesses of particles. Different coatingthicknesses can be applied such as by varying the sweep speed of thesubstrate relative to the particle nozzle, by making multiple sweeps ofportions of the substrate that receive a thicker particle coating or bypatterning the layer, for example, with a mask.

Thus, layers of materials, as described herein, may comprise particularlayers that do not have the same planar extent as other layers. Thus,some layers may cover the entire substrate surface or a large fractionthereof while other layers cover a smaller fraction of the substratesurface. In this way, the layers can form one or more localized devices.At any particular point along the planar substrate, a sectional viewthrough the structures may reveal a different number of identifiablelayers than at other point along the surface. Generally, for opticalapplications, the particle coatings of a particular optical layer have athickness in the range less than about 500 microns, in otherembodiments, in the range less than about 250 microns, in additionalembodiments in the range(s) from about 50 nanometers to about 100microns and in further embodiments in the range(s) from about 100nanometers to about 50 microns. A person of ordinary skill in the artwill recognize that additional range(s) within these explicit ranges andsubranges are contemplated and are encompassed within the presentdisclosure.

Consolidation to Form Optical Materials

Heat treatment can melt and fuse the particles and lead to compaction,i.e., densification, of the powders to form the desired material, suchas an optical material. This fusing of the particles is generallyreferred to as consolidation. To consolidate, i.e., densify, the opticalmaterials, the materials can be heated to a temperature above themelting point or the flow temperature, i.e., softening point, of thematerial to consolidate the coating into a smooth uniform material.Consolidation can be used to form amorphous or crystalline phases inlayers. In general, consolidation can be performed before or afterpatterning of a layer. Using the techniques described herein, dopedglasses can be formulated into planar optical devices.

Generally, the heating is performed under conditions to melt theparticles into a viscous liquid. To form the viscous liquid, crystallineparticles are heated above their melting point and amorphous particlesare heated above their softening point. Because of the high viscosity,the material does not flow significantly on the substrate surface.Processing at higher temperatures to reduce the viscosity of the meltcan result in undesirable melting of the substrate, migration ofcompositions between layers or in flow from a selected area of thesubstrate. The heating and quenching times can be adjusted to change theproperties of the consolidated coatings, such as density. In addition,heat treatment can remove undesirable impurities and/or change thestoichiometry and crystal structure of the material.

Following deposition of the powder layer, the precursors can be shut offsuch that the reactant stream only comprises a fuel and an oxygen sourcethat reacts to form a product without particles. The flame resultingfrom the reaction of the fuel and oxygen source can be used to heat thecoated substrate. Such a heating step can reduce additive/dopantmigration upon full consolidation of a doped silica glass. A preliminaryheat treatment can be applied with the reactor flame to reduce dopantmigration during the consolidation process. A flame heating step can beperform between coating steps for one or more layers prior to a heattreatment to fully consolidate the material.

Suitable processing temperatures and times generally depend on thecomposition of the particles. Small particles on the nanometer scalegenerally can be processed at lower temperatures and/or for shortertimes relative to powders with larger particles due to lowermelting/softening points for the nanoparticles in comparison with bulkmaterial. However, it may be desirable to use a comparable meltingtemperature to obtain greater surface smoothness from improved meltingof the nanoparticles.

For the processing of silicon oxide nanoparticles, the particle coatingscan be heated to a temperature from about 800° C. to 1700° C., althoughwith silicon substrates the upper limit is about 1350° C. Highertemperatures can be reached with appropriate ceramic substrates. Dopantsin the silicon oxide particles can lower the appropriate consolidationtemperatures. Thus, the dopant can be selected to flow into a uniformoptical material at a lower temperature. Suitable dopants to lower theflow temperature when placed into silicon oxide (SiO₂) include, forexample, boron, phosphorous, germanium, and combinations thereof. Theamount and composition of one or more dopants can be selected to yield adesired flow temperature for consolidation and index-of-refraction ofthe consolidated optical material.

Heat treatments can be performed in a suitable oven. It may be desirableto control the atmosphere in the oven with respect to pressure and/orthe composition of the gases. Suitable ovens comprise, for example, aninduction furnace or a tube furnace with gas flowing through the tube.The heat treatment can be performed following removal of the coatedsubstrates from the coating chamber. In alternative embodiments, theheat treatment is integrated into the coating process such that theprocessing steps can be performed sequentially in the apparatus in anautomated fashion.

For many applications, it is desirable to apply multiple particlecoatings with different compositions. In general, these multipleparticle coatings can be arranged adjacent to each other across the x-yplane of the substrate being coated (e.g., perpendicular to thedirection of motion of the substrate relative to the product stream), orstacked one on top of the other across the z plane of the substratebeing coated, or in any suitable combination of adjacent domains andstacked layers. Each coating can be applied to a desired thickness.

For optical applications in some embodiments, silicon oxide withdifferent additive/dopant composition and/or concentration can bedeposited adjacent each other and/or in alternating layers.Specifically, two layers with different compositions can be depositedwith one on top of the other, and or additionally or alternatively, withone next to the other, such as layer A and layer B formed as AB. Inother embodiments, more than two layers each with different compositionscan be deposited, such as layer A, layer B and layer C deposited asthree sequential (e.g., stacked one on top of the other, or adjacent tothe other, or adjacent and stacked) layers ABC. Similarly, alternatingsequences of layers with different compositions can be formed, such asABABAB . . . or ABCABCABC . . . . Thus, by varying composition/opticalproperties along layers and/or between layers complex variation ofoptical properties can be accomplished along all three dimensions of anoptical structure.

Individual layers, such as uniform layers, after consolidation generallyhave an average thickness in the range of less than 100 microns, in manyembodiments in the range from about 1 micron to about 50 microns, inother embodiments in the range from about 3 microns to about 20 microns.A person of skill in the art will recognize that ranges within thesespecific ranges are contemplated and are within the scope of the presentdisclosure. Thickness is measured perpendicular to the projection planein which the structure has a maximum surface area.

The material with multiple particle coatings can be heat treated afterthe deposition of each layer or following the deposition of multiplelayers or some combination of the two approaches. The optimal processingorder generally would depend on the melting point of the materials.Generally, however, it is desirable to heat treat and consolidate aplurality of layers simultaneously. Specifically, consolidating multiplelayers simultaneously can reduce the time and complexity of themanufacturing process and, thus, reduce manufacturing costs. If theheating temperatures are picked at reasonable values, the meltedmaterials remain sufficiently viscous that the layers do not mergeundesirable amounts at the interface. Slight merging of the layersgenerally does not affect performance unacceptable amounts. By changingreaction conditions, particles can be deposited with changing particlesize in the z-direction within a single layer or between layers. Thus,smaller particles can be deposited on top of larger particles. Since thesmaller particles generally soften at lower temperatures, theconsolidation of the upper layer can be less likely to damage the lowerlayers during the consolidation step. To form patterned structuresfollowing deposition, patterning approaches, such as lithography andphotolithography, along with etching, such as chemical etching orradiation-based etching, can be used to form desired patterns in one ormore layers. This patterning generally is performed on a structure priorto deposition of additional material. Patterning can be performed onparticle layers or consolidated layers.

Integrated Gradient Index Lenses

Gradient index lenses can be incorporated into optical structures.Generally, the optical structures are integrated with other opticaldevices within the structure. The optical structures can be, forexample, planar optical structures or optical fibers. The gradient indexlenses can have an index-of-refraction that varies in one dimension orin two dimensions. By forming the gradient index lens directly into anintegrated optical structure, the optical material forms a continuousmaterial that does not have abrupt interfaces.

With respect to gradient index lenses with index gradients in twodimensions, the index-of-refraction varies with the radial distance froma central axis of the lens. The orientation of a gradient index lenswith a radial variation in index-of-refraction is shown in FIG. 14. Asshown in FIG. 14, the central axis is marked C and the radial directionis noted along a ray from the central axis. Light generally propagatesthrough the lens with a component along the central axis.

While other functional dependences can be used, a quadratic drop inindex-of-refraction with distance from the central axis results in agradient index lens with optical properties of a conventional concavelens. For gradient index lenses with a variation in index-of-refractionapproximating a quadratic function, the parabolic function describingthe index-of-refraction distribution has a steepness that is describedby the gradient constant, A. Although the gradient constant of an actualgradient index lens can be determined through indirect measurementtechniques, the gradient constant characterizes a lens' opticalperformance. Specifically, the focusing properties for a particularwavelength of light depends on the value of the gradient constant. Thedependence of the gradient constant on wavelength can be determined. Thedispersion equation for a gradient index lens depends on the diameterand the numerical aperture of the lens.

Light passing through a gradient index lens is refracted due to thechanging index-of-refraction. To evaluate the refraction, a particularlight ray follows a sinusoidal path through an ideal gradient indexlens. Light that has traversed one cycle of the sinusoidal wave thatcharacterizes the lens is indicated to have traversed one pitch. Thepitch (P) can be related to the mechanical length of the lens (Z) andthe gradient constant according to the following equation: 2πP=√{squareroot over (A)}−Z. The mechanical length Z is marked in FIG. 14 for therepresentative lens in the figure. FIGS. 15-19 illustrates particularlight ray trajectories for gradient index lenses of various pitchvalues, P=0.25 object at infinity, P=0.5 object at front surface, P=0.75object at infinity and P=1 object at front surface.

In contrast with conventional gradient index lenses, alternativeembodiments of gradient index lenses have an index-of-refraction thatvaries in only one dimension. Thus, the index-of-refraction decreasesrelative to a central plane. Two alternative configurations forone-dimensional gradient index lenses on a planar surface are shown inFIGS. 19 and 20, with the central plane noted by C.P. and the distance dfrom the central plane is noted with rays.

While other function variation in index-of-refraction can be used,one-dimensional gradient index lenses that have an index-of-refractionthat varies quadratically with distance from the central plane haveoptical properties analogous to conventional cylindrical lenses.Gradient index lenses with variation in index-of-refraction inone-dimension correspondingly bend light in only one dimension. Bendinglight in one dimension is suitable for integrating optical devices on asubstrate surface. A one-dimension gradient index lens can counteractspread due to the numerical aperture at the surface of an opticaldevice. Thus, these one-dimensional gradient index lenses are effectiveat coupling optical devices within an integrated optical circuit. Thegradient index lens can be integrated with other optical devices duringthe formation of the optical circuit by forming the gradient index lensalong with the other optical devices during the production process.

Ideal gradient index lenses provide smoothly varying light raytrajectories within the gradient index media. The paraxial orfirst-order behavior of gradient index materials can be modeled byassuming sinusoidal light ray paths within the lens. In alternativeembodiments, the ideal variation in index-of-refraction can beapproximated, for example, with a step-wise variation or other variationthat is not precisely the quadratic variation. For these embodiments,light ray trajectories can be approximated with sinusoidal trajectoriesor simulation programs can be used based on a more realistic descriptionof the index-of-refraction variation. In further embodiments, otherfunctional dependence of the variation in index-of-refraction can beused rather than a quadratic dependence. For these embodiments, thetrajectories of light rays can be simulated using appropriate simulationprograms.

For the formation of integrated gradient index lenses, the gradientindex lens generally is connected on either side or both sides with anoptical device. the gradient index lens can be integrated within anoptical circuit in either a fiber structure or a planar structure. Anexample of a fiber structure with an integrated gradient index lens isshown in FIG. 21. As shown in FIG. 21, optical fiber element 350comprises an optical amplifier 352, a gradient index lens 354 and atransmission fiber 356. Optical amplifier 352 generally comprises a core358 surrounded by a cladding 360 in which the core comprises anamplifying optical material that absorbed energy to amplify a signalfrom an amplifying energy source optically coupled to the amplifyingoptical material. Transmission fiber 358 comprises a core 362 andcladding 364 with approximately constant index-of-refraction. Gradientindex lens 354 connects optical amplifier 352 and transmission fiber356. Gradient index lens 354 can limit spreading and loss of lighttransmitted between optical amplifier 352 and transmission fiber 356.Gradient index lens 354 can be a one-dimensional or a two-dimensionalgradient index lens.

As described below, planar optical structures and optical fiber preformscan be formed on a substrate. The substrate, for example, can be formedfrom silicon. Common substrates are round wafers, although substratesthat are square or other shapes can be used. For the formation ofpreforms, it may be desirable to shape the substrate highly elongated inone dimension. The aspect ratio may range from about 1:5 to about 1:50,or in other embodiments from about 1:10 to about 1:25. A person ofordinary skill in the art will recognize that ranges and subrangeswithin these explicit ranges are contemplated and are within the presentdisclosure. Similarly, for preforms it may be desirable to have coatingswith dimensions that change as further coatings are added such that thefinal structure does not have a rectangular shape to facilitate pullingof the fiber from the preform. The formation of a gradient index lens inan optical fiber can be based on known geometric changes that occur uponthe pulling of the fiber from the preform. The preform is softened byheating to form a viscous material that can be pulled to form the fiber.The formation of gradient index lenses in optical fibers is describedfurther in U.S. Pat. No. 3,941,474, incorporated herein by reference.

In other embodiments, the gradient index lenses are integrated intoplanar optical structures. Generally, planar integrated opticalstructures are located on the surface or a planar substrate. However,substrateless planar structures are also contemplated. The formation ofsubstrateless planar optical structures is described in copending andcommonly assigned U.S. patent application Ser. No. 09/931,977, now U.S.Pat. No. 6,788,866 to Bryan et al., entitled “Layer Materials And PlanarOptical Devices,” incorporated herein by reference. For substratelessembodiments, a projection of the planar device to obtain a maximum areaprovides a planar extent of the device. This projected planar extentestablishes a plane analogous to the substrate surface for orienting aposition along the planar surface.

For each set of core and cladding refractive indices, there is a narrowrange of core diameters that will propagate the fundamental mode of agiven wavelength with a low loss, but not allow any higher-order modes.The refractive-index difference also determines the range of angles atwhich incident light can continue to propagate down the guide.Therefore, the choice of wavelength and index-of-refraction differencedetermines the acceptance angle and optimum core size, as well as thespot size and divergence of the lowest-loss propagating beam. Thedifferent optical materials used for different components often differin desirable spot-size and divergence angle, although the product ofsize times angle tends to be close to a constant. For example, somedevices such as a single mode optical fiber have a larger desired spotsize and a smaller divergence angle, whereas other optical devices, suchas some gain blocks or small-bend-radius arrayed waveguide grating(AWG), have a smaller spot size and a larger divergence angle. If twooptical devices with different optimal beam characteristics are simplybutted together, an undesirable amount of light is lost at theinterface, even if the materials are fused together or are codeposited.

Lenses can be used to convert one set of values for spot size andacceptance angle to one another with reduced loss. A gradient index lensintegrated into an optical fiber or planar optical structure wouldfunction in the same way with all of the advantages of a gradient indexlens over a conventional lens. By converting the output of one sectionof waveguide to a lower loss input parameters of the next section of anintegrated system, no extra losses result that correspond to losses froma conventional lens that introduce extra surfaces.

In some applications, it is desirable to incorporate into an integratedstructure both glass/amorphous materials and crystalline materials,single crystalline or polycrystalline. In particular, many waveguides,couplers, amplifiers and the like can be formed from silica-basedglasses or other glass forming optical materials. It can be difficult togrow the crystals on a passive substrate. An alternative would be toplace high quality crystalline sections of material into a glassstructure. An advantage of using an integrated gradient index lens toconnect a glass and crystalline material is that light transmittedthrough the crystalline material can be at least partly collimated withthe lens prior to reaching the crystalline material. Most effects thatoccur in crystalline materials are angle sensitive. Collimated light canpropagate at the same angle if the crystal is oriented to line up withthe collimated beam. Any optical functions of the crystalline materialcan be more efficient with collimated light. Also, a similar gradientindex lens receiving light from the crystalline material can reduce lossby collecting more light than a core end of a waveguide.

Similarly, other free space optical elements in general can beintegrated into an optical structure, either a fiber based structure ora planar structure, by forming a cut out in the optical structure, forexample, by etching. The free space optical element, such as a filter,grating, or the like, is then inserted into the cut out. The use of agradient index lens is an alternative to using an external microlens tofocus or collimate the light beam between the optical devices within themonolithic optical structure and the free space optical devices. The useof the gradient index lens results in the advantages discussed above andbelow.

A representative example of a planar optical structure is shown in FIG.22. As shown in FIG. 22, integrated optical circuit 380 includes aplanar waveguide 382, a gradient index lens 384 and an optical coupler386 on a substrate 388. Examples of one-dimensional gradient indexlenses are shown in sectional views in FIGS. 23 and 24, and an exampleof a two-dimensional gradient index lens is shown in a sectional view inFIG. 25.

Referring to FIG. 23, gradient index lens 400 is adjacent substrate 402.A central plane 404 is noted with phantom lines. The index of refractionvaries along rays marked d. Cladding 406 with a lower index ofrefraction than the index at the central plane generally is locatedadjacent gradient index lens 400. Optionally, cladding can be includedabove and/or below gradient index lens 400.

Referring to FIG. 24, gradient index lens 420 is located on anunder-cladding 422 which is adjacent a substrate 424. An over-cladding426 can be placed on top of gradient index lens 402. Generally, cladding428 is adjacent gradient index lens 420. Gradient index lens 420 has aone-dimensional variation in index-of-refraction with a central plane430 noted in phantom lines. Cladding 428, under-cladding 422 andover-cladding 426 generally have an index-of-refraction lower than theindex-of-refraction at central plane 430 of gradient index lens 402.Gradient index lens 420 has an orientation orthogonal to gradient indexlens 400 in FIG. 23.

Referring to FIG. 25, gradient index lens 440 has a radially varyingindex-of-refraction. The index-of-refraction varies radially fromcentral axis 442. Gradient index lens 440 is adjacent substrate 444 andis surrounded by cladding 446. An optional layer of over-cladding and/orunder-cladding can be placed respectively over or under gradient indexlens 440. The radial variation in index-of-refraction can be truncatedwith plans of cladding or the like without significantly alteringperformance of the lens.

It may be desirable to place two one-dimensional gradient index lenseswith orthogonal variation in index-of-refraction adjacent each otheralong an integrated topical pathway, such as a fiber or a planarintegrated structure. One of the one-dimensional gradient index lensesfocuses light in a first dimension while the other lens can focus thelight in the orthogonal dimension. Generally, the gradient index lensescan be placed in either order. The formation of two gradient indexlenses may be easier to accomplish than the formation of a gradientindex lens with radial variation in index of refraction whileaccomplishing a similar result. If desired, a waveguide can be placedbetween the two gradient index lenses.

Referring to FIG. 26, an integrated optical structure 460 comprises afirst gradient index lens 462, a second integrated index lens 464separated by an optional waveguide 466 with appropriate core andcladding. First gradient index lens 462 has a central plane 468 parallelto substrate surface 470, and second gradient index lens 464 has acentral plane 472 perpendicular to substrate surface 470. Integratedoptical structure 460 can comprise additional optical devices 474, 476,as desired.

An embodiment of an optical structure with gradient index lensescoupling optical elements of a monolithic optical structure with freespace optics are shown in FIG. 27. Optical structure 500 includes afirst waveguide core 502 and a second waveguide core 504 integratedwithin a monolithic structure. Cladding 506, 508 surround firstwaveguide core 502, and cladding 510, 512 surround second waveguide core504. Gradient index lens 514 is optically coupled to first waveguidecore 502, and second gradient index lens 516 is optically coupled tosecond waveguide core 504. Free space optical element 518 is located incut out 520 between first gradient index lens 514 and second gradientindex lens 516. Free space optical element 518 optically connects firstgradient index lens 514 and second gradient index lens 516. Opticalstructure 500 can be a planar optical structure or a fiber-based opticalstructure. Only one or more than two gradient index lenses can beforming into the integrated optical structure. In addition, the opticalstructure can comprise other and/or additional optical devices.Similarly, cores 502, 504 can be replaced with active optical devicesand/or other optical devices of interest.

Alignment sensitivity can be a major source of insertion loss incomponent coupling. Conventional single-mode waveguide/optical fibercores are a few microns in diameter. For these cores, alignment withintens to hundreds of nanometers is used to obtain low-loss coupling. Ifthe beams are collimated to a larger to a larger size than the core,position sensitivity is reduced. An integrated lens can be a convenienttool for performing the desired collimation.

In addition, the gradient index lenses can be incorporated as acomponent into more involved devices. For example, some planar opticaldevices, such as Echell gratings, incorporate a curved surface to focuslight. These curved surfaces can be incorporated into an etch pattern.If a smooth surface is needed, the etching process can be very expensivebecause a smooth curve has a high resolution. Particularly if the curveis aspheric to minimize aberrations and produce tightly focused spots,the etching can be both difficult and expensive. A gradient index lenscan produce the same effect as a curvature such that a properly placedgradient can enable the devices to function as if some surfaces werecurved. However, the gradient index lenses can be produced with muchsimpler processing approaches, either etching along straight linesand/or formation of the gradient during the deposition process. Echellegratings are described further in U.S. Pat. No. 6,339,662 to Koteles etal., entitled “Wavelength Stabilized Planar Waveguide Optical DevicesIncorporating A Dispersive Element,” incorporated herein by reference.

Similarly, delay lines can be used in planar optical devices tocompensate for chromatic dispersion. In some embodiments, a delay linehas a straight waveguide for the slowest traveling wavelength bands, andwaveguides with bends to increase the path length for the fastertraveling wavelength bands. The curved waveguides are more difficult toform by lithography or the like and take up more area on the substrate.Also, the curved waveguides can incur greater loss for a given error inindex-of-refraction or sidewall roughness. Delay lines can be formedthat are all straight using a gradient index lens. The delay linesinvolve changes in index-of-refraction that result different propagationtimes. The gradient index lens can be used to effectively couple thematerials with the different indices-of-refraction.

Formation of Gradient Index Lenses

One-dimensional gradient index lenses and two-dimensional gradient indexlenses can be formed by light reactive deposition in planar and opticalfiber preform configurations. In some embodiments, the variation inindex-of-refraction can be generated by variation in dopantconcentrations. For example, a dopant that decreases index-of-refractioncan be placed in gradually increasing amounts along the direction ofdecreasing index-of-refraction. Alternatively or additionally, a dopantthat increases index-of-refraction can be placed in gradually decreasingamounts along a direction of decreasing index-of-refraction.

In some embodiments, dopants are introduced following formation of anoptical structure by generating a porosity in the structure andcontacting the structure with a compound comprising the dopant. Inparticular, powder array are inherently porous and can be contacted withappropriate dopant compositions prior to consolidation. However, theproduction of a composition gradient can involve careful control of theintroduction of the dopant to the optical structure. Above, the use oflight reactive deposition was described for the placement of desiredcompositions at selected locations within a three dimensional opticalstructure. This approach can be used to introduce an gradient in dopantlevels particularly suitable for the formation of gradient index lenses.In particular, dopant levels can be changed gradually during thedeposition process by appropriately changing the flow of dopantprecursor in the reactant stream. A small gradual change in dopantprecursors during the deposition process generally does not change theparticle production process. With or without the use of masks, thedesired compositions can be deposited by adjusting the composition andspeed of moving the substrate through the product particle flow. Thecomposition within the powder array can be selected such that thedesired composition distribution is obtained following consolidation,i.e., densification.

As utilized herein, the term “in the range(s)” or “between” comprisesthe range defined by the values listed after the term “in the range(s)”or “between”, as well as any and all subranges contained within suchrange, where each such subrange is defined as having as a first endpointany value in such range, and as a second endpoint any value in suchrange that is greater than the first endpoint and that is in such range.

Light, e.g., ultraviolet or visible light, can also be used to alter theindex-of-refraction. In particular, germanium containing glasses canundergo permanent changes in index-of-refraction as a result ofillumination with light of appropriate wavelength and intensity.Specifically, germanium oxide and germanium doped silica are suitableoptical materials. A pulsed excimer (KrF) laser produces suitableoptical wavelength. The light can be focused to different positionswithin the optical material to vary the index-of-refraction as afunction of depth within the optical material. The light can besimilarly focused according to other geometries to introduce desiredgradients in index-of-refraction. The variation in index-of-refractionof a material using light is described further in copending and commonlyassigned PCT application designating the U.S. serial numberPCT/US02/01702 to Bryan et al., entitled “Optical Materials WithSelected Index Of Refraction,” incorporated herein by reference.

The embodiments described above are intended to be illustrative and notlimiting. Additional embodiments are within the claims below. Althoughthe present invention has been described with reference to specificembodiments, workers skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scopeof the invention. In addition, the terms including, comprising andhaving as used herein are intended to have broad non-limiting scope.

1. An optical structure comprising a first optical core, a secondoptical core, a gradient index lens and a free space optical element,wherein the first optical core, the second optical core and gradientindex lens are within a monolithic optical structure and the free spaceoptical element is within a cut out in the monolithic optical structureand wherein the gradient index lens is optically connected with thefirst optical structure and the free space optical element located inthe optical path connecting the first optical core and the secondoptical core.
 2. The optical structure of claim 1 wherein the gradientindex lens comprises a gradient in index-of-refraction in twodimensions.
 3. The optical structure of claim 1 wherein the gradientindex lens comprises a gradient in index-of-refraction in one dimension.4. The optical structure of claim 3 wherein the gradient is along anaxis perpendicular to a plane orienting the structure.
 5. The opticalstructure of claim 3 wherein the gradient is along an axis parallel to aplane orienting the structure.
 6. The optical structure of claim 1wherein the gradient comprises a step-wise gradient inindex-of-refraction.
 7. The optical structure of claim 1 wherein thegradient comprises a continuous change in index-of-refraction.
 8. Theoptical structure of claim 1 wherein the monolithic optical structure isa planar optical structure and wherein the second optical core has adifferent thickness perpendicular to a plane orienting the structurerelative to the thickness of the first optical core.
 9. The opticalstructure of claim 1 wherein the monolithic optical structure is aplanar optical structure and wherein the second optical core has a widthdifferent from the width of the first optical core, wherein the width isalong an axis parallel to a plane orienting the structure andapproximately perpendicular to a light propagating direction through thefirst optical core and the second optical core.
 10. The opticalstructure of claim 1 wherein the monolithic optical structure is aplanar optical structure and wherein the second optical core has athickness and width each different from that of the first optical corecore, wherein the thickness is along an axis perpendicular to a planeorienting the structure and wherein the width is along an axis parallelto a plane orienting the structure and approximately perpendicular to alight propagating direction through the first optical core and thesecond optical core.
 11. The optical structure of claim 1 wherein thegradient index lens comprises silica glass.
 12. The optical structure ofclaim 11 wherein the gradient in index-of-refraction corresponds with agradient in composition of the silica glass.
 13. The optical structureof claim 1 wherein the free space optical element comprises a filter ora grating.
 14. The optical structure of claim 1 wherein the gradientindex lens optically connects the first optical core and the free spaceoptical element.
 15. The optical structure of claim 14 furthercomprising a second gradient index lens within the monolithic structureoptically connecting the free space optical element and the secondoptical core.
 16. An optical fiber comprising a first gradient indexlens and a cladding, the first gradient index lens having anindex-of-refraction varying in a single dimension relative to a centralplane along a first axis and the cladding being located at least alongthe edges of the central plane wherein the cladding has anindex-of-refraction lower than the gradient index lens along the centralplane.
 17. The optical fiber of claim 16 wherein the gradient index lensis optically connected to a first core and a second core wherein thefirst core and the second core have different diameters.
 18. The opticalfiber of claim 16 further comprising a second gradient index lens inoptical communication with the first gradient index lens.
 19. Theoptical fiber of claim 18 wherein the second gradient index lens has anindex of refraction varying in a single dimension along a second axisthat is not parallel to the first axis.
 20. The optical fiber of claim16 wherein the gradient index lens comprises glass.